Conventionally employed for installing this type of valve is a gas container valve fastening machine which comprises a column erected on a base, a clamp unit for securely supporting a gas container placed on the base in an upright posture parallel to the column, a rotary drive unit vertically movably disposed above the clamp unit along the column, a rotary transmission unit interlocked and connected to an output shaft of the rotary drive unit, and a wrench attached to a lower end of the rotary transmission unit, wherein a valve engaged in the wrench is rotated by the rotary drive unit and threaded into a screw hole formed in a sleeve of the gas container.
When the male screw portion of the valve is threaded into a screw hole of a sleeve of the gas container main body by using such a conventional valve fastening machine, the valve moves in the axial direction just by one pitch of the screw thread every turn of the male screw portion of the valve, but in case the valve is unable to smoothly move in the axial direction due to frictional forces between the valve and the wrench, there arises such a problem that the male screw portion of the valve or the screw thread of the sleeve is damaged by surface pressures generated at one side of the screw thread engaged therewith or gas leakage trouble resulting in defective fastening due to a gap formed at the other side of the screw thread.
In order to solve such a problem caused due to defective fastening, a valve fastening machine is proposed in Patent document 1 (Japanese Patent Publication No. 2813765), which is configured in that the output shaft of a rotary drive unit used for turning a wrench is connected to a transmission member with a wrench attached thereto in such a manner as to be unable to rotate individually and free to move in the axial direction, and also there is provided a spring which presses the transmission member against the output shaft with a predetermined pressure.